Learning how to safely view the Great American Eclipse

Pop quiz: What do you know about a solar eclipse?

If you were in the group of people at the Franklin Institute on Sunday learning how to host an eclipse viewing party from the museum’s own sun god, chief astronomer Derrick Pitts, quite a bit.

An eclipse occurs when the moon blocks the sun. It’s rare. It’s not always complete.

All correct, said Pitts, who led the 2½-hour workshop for representatives of schools, a church, a library, and a nature center in preparation of the Great American Eclipse, which will cut a swath of total darkness across parts of the United States, traveling eastward from coast to coast, on Aug. 21.

Pitts then boiled down the astronomical phenomenon to its essentials: “It’s nothing but light and shadow.”

Franklin Institute chief astronomer Derrick Pitts (center) explains how to use a Sunspotter telescope to view the solar eclipse to (from left) Sarah Winchowky and Raven Wylde from the Free Library and David Bungard with the Vaux Big Picture school. (CLEM MURRAY / Staff Photographer)

In Philadelphia, alas, expect more light than shadow. This region is outside the 70-mile-wide arc that the eclipse will follow across the country. With the moon covering only 80 percent of the sun in our area, “it will look like a cloudy day,” Pitts said.

Not exactly the awe-inspiring experience that people in, say, South Carolina — the closest state to us with total coverage — will get to experience.

But the dozen amateur astronomers in the class didn’t seem to mind.

“I’m not discouraged at all,” said Barbara Sharpe, science department head at Esperanza Academy Charter School in Hunting Park and an eighth-grade teacher. “You can still watch the moon move across the sun, and that in itself is exciting.”

When she was a kid, she saw several partial eclipses, viewing them through homemade pinhole cameras, and thought they were amazing.

Now she plans to do the same with her students and expects them to be just as wowed.

“Our society has gotten hectic and crazy in recent days,” she said. “I’m trying to slow down and watch this really amazing thing happening in the sky using this pinprick through paper. The kids are going to love it.”

Pitts started by leading the group to the rooftop of the institute so they could look at the sun through a solar viewer. That’s the other thing about an eclipse, he warned over and over and over: “If you look at it, you will go blind.”

With magnifying glasses, the class tried to burn holes in a piece of paper. Then, using Sunspotters, they were able to reflect the sun, including sunspots and passing clouds, on paper.

Pitts used human models, i.e. the workshop members, to show the orbits of the moon, Earth, and sun, and how they line up to cause an eclipse.

Then he unleashed some facts about the sun-blocking events: There are two a year somewhere on the planet; the last total solar eclipse over Philadelphia occurred in 1478,  the next will be on May 1, 2079, and the one after that in 2144. The next total solar eclipse over the U.S. will be in 2024. The Great American Eclipse will start at 1:21 p.m., peak at 2:44, end by 4:01.

How, Pitts asked, can the moon, which is 2,100 miles in diameter, block the enormous sun, which is 864,000 miles in diameter? The answer is that the sun is 400 times farther from the Earth than the moon and 400 times bigger than the moon. The result is that from Earth, they appear to be the same size.

“Everybody’s enthusiastic about this stuff,” said Pitts, who plans to watch from St. Joseph, Mo., where 100,000 people are expected to tilt their heads toward the sky — wearing protective glasses, of course — to see a total eclipse of the sun.

Fanny Tan (left), a teacher at Cheltenham High School, and Barbara Sharpe, a teacher at Esperanza Academy Charter School, carry Sunspotter solar telescopes as the participants in an eclipse workshop at the Franklin Institute head to the roof.

For those hosting local events, like Zion Baptist Church in North Philadelphia and Riverbend Environmental Education Center in Gladwyne, Pitts — astronomer, Fels Planetarium director, NASA solar system ambassador — morphed into a third-grade teacher and taught them how to use construction paper, aluminum foil, a mirror, and a shoe box to make various viewing devices.

David Bungard, a science adviser for Philadelphia’s new Vaux Big Picture high school, which opens in August and where learning will be all project-based, said he plans to take his 7-year-old son and some friends to Marconi Plaza in South Philadelphia for the big event.

“It’s still pretty cool to watch the moon, even if it’s not 100 percent, traverse across the sun,” he said. “I love science and teaching science, so it’s a good opportunity to give people that information.”

Which is exactly what Pitts wanted the science lovers in the class to do. Get people together, plan where you’ll watch, be prepared to move to a better location, have your viewing contraptions ready to go. Then “forget the mechanics and all that other stuff,” he said. “Enjoy the experience.”

One more thing, Pitts said: Check the weather forecast. “If it’s cloudy, you can’t see anything.”